Th DragonFly BSD team has released DragonFly BSD 2.2. The biggest improvement in this release is that the HAMMER filesystem is considered production ready, but there is a whole boatload of other improvements as well.

I wouldn't say that HAMMER would be a good replacement for ZFS (though I haven't done extensive testing of HAMMER like I have of ZFS), but it is a good file system. here are teh baisc goals of HAMMER

Instant or nearly-instant mount. No fsck needed on crash recovery.
• Full history retention with easy access, via the live file-system. That means
being able to CD into snapshots of the file-system and being able to access
previous versions of a file (or directory tree), whether they have been
deleted or not.
• Good performance.
• Queue-less, incremental mirroring.
• Ability to re-optimize the layout in the background, on the live file-system.
• No i-node limitations.
• Extensible media structures to reduce compatibility issues as time
progresses.
• Support for very large file-systems (up to 1 exabyte)
• Data integrity checks, including high-level snapshot tar md5s.
• Not hamstring a clustered implementation, which has its own list of
requirements.
• Not hamstring a remote access implementation.